Abstract
Flower strips are an effective agri-environmental measure to promote functional biodiversity and ecosystem services in agricultural landscapes. In particular, tailored annual flower strips are increasingly implemented to foster insect pollination and biological pest control. While positive effects of flower strips on service providers and associated ecosystem services were recently demonstrated, little is known about how their effectiveness is affected by the surrounding landscape. We investigated how landscape composition and configuration, as well as flower strip traits influence the abundance of all insects, pollinators and natural enemies in 74 annual flower strips across 7 years (2014–2020). Landscape characteristics such as crop diversity, mean field size, area, and quality of semi-natural farmland habitats were assessed in a 1-km radius surrounding flower strips and combined with flower strip traits such as size, flower coverage, and flowering plant species richness to model insect abundance and diversity. Total insect and pollinator abundance, as well as wild bee abundance, richness, and diversity in flower strips were negatively affected by the share of semi-natural farmland habitats in the surrounding landscape, suggesting a dilution effect. On the other hand, semi-natural habitats with elevated ecological quality (i.e., biodiversity promotion areas with high botanical and structural diversity) enhanced total insect and pollinator abundance in flower strips. Furthermore, pollinator abundance and wild bee abundance in specific were positively affected by the flower coverage of the strips. Our results therefore suggest simultaneous competition and facilitation effects of semi-natural habitats on the landscape scale depending on their ecological quality. Annual flower strips will therefore be most effective in fostering services in landscapes of moderate to low complexity but with a high share of semi-natural habitats with increased ecological quality. For additional benefits for pollinator and wild bee abundance, flower strips should be designed to yield high flower cover. Our study thus highlights the importance of quality of ecological infrastructure and provides recommendations to maximize ecosystem services and biodiversity by means of flower strips at the landscape scale.
Highlights
The ongoing agricultural intensification has resulted in severe declines of farmland biodiversity and associated ecosystem services (Robinson and Sutherland, 2002)
While all investigated groups and indices except natural enemies were negatively influenced by the area of biodiversity promotion areas (BPA) in the surrounding landscapes, BPA with elevated ecological quality had a positive effect on the abundance of total insects and pollinators in specific
Our results provide evidence that both flower strip traits and landscape characteristics are important for the abundance of insects overall and different functional groups in annual flower strips
Summary
The ongoing agricultural intensification has resulted in severe declines of farmland biodiversity and associated ecosystem services (Robinson and Sutherland, 2002). Beyond the increase in external inputs such as fertilizers and pesticides, the simplification of the agricultural landscapes was identified as the predominant driver of these declines This includes increases in average field size, reduction in land-use diversity, and crop rotation, as well as the removal of natural and seminatural habitats such as hedges, waterbodies or small structural elements (Stoate et al, 2001). To counteract these declines, agrienvironmental schemes (AES) were implemented across Europe, after the reform of the Common Agriculture Policy in 1992 (Herzog et al, 2017). The basic concept of annual flower strips is that pollinators and natural enemies are attracted to the flower strips from where they spill-over to adjacent agricultural crops to enhance the respective services (Tschumi et al, 2015; Tschumi et al, 2016; Albrecht et al, 2020)
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